Hey, so I'm trying to sub-out the LM394 for the VCA/VCO and was wondering if it would be possible to use a JFET LSK389 instead of something like the SSM2210 which is expensive and harder to find.. thoughts?

I don't think you can use a jfet to replace the LM394/SSM2210 - the schematic is the usual two npn exponential converter. But you easily use two matched discrete transistors. There's a thread where Ian Fritz gives a very simply method of hand matching (http://electro-music.com/forum/viewtopic.php?highlight=transistor+ian&t=18365)

The dual transistor problem is one we all face. You either have to match those trannies yourself or just bite the bullet and pay for something you can trust. I don't think there's a magic solution available.

One thing to think about. Frequency tracking is the single most important quality when determining if a VCO is useful or not. Your ear can easily detect tracking and drift problems. The matched trannies are the single most important part of that function. So - if you're going to spend too much money on anything, the trannies are the place to do it.

There are some subs currently in production, but they are quite expensive.
I've used some MAT12 (free samples ) in the Yusynth VCO's and they worked perfect. I don't remember other references but I know they exist even if the MAT12 is the easiest to get.

so i ended up caving and buying some ssm2210s from bridechamber. those should work nicely. My new question regards one of the transistors on the CGS VCO - the 2N4856. is this thing necessary if I don't plan on using the Sync function? based on some assistance looking at the schematic it appeared that this was all that it was doing, however i could way off. has anyone built this thing without the 2N4856?

thanks for the quick reply! i guess i should bite the bullet and stop trying to cut corners.

I used to do exactly the same thing. Then I went about it a different way. I found that there are some things you can save large amounts of money on if you plan to build a bunch of equipment.

Take resistors for instance. I found a chinese place on Ebay that will sell you 1000s of them for almost nothing. You get 40 or 50 each of a wide range of values. Some of them you'll never use, but it still makes financial sense.

For values you use all the time (1M, 100K etc) I go to mouser and buy 200 of them for $4. The quantity discounts are absolutely insane. I also buy most transistors and diodes in large quantity.

IC sockets from China - they work fine and are very low cost.

Switches? NO - you get what you pay for there.

Caps- for typical ceramic discs I go to Chinese companies again. Big bags of them for almost nothing.

There are a lot of things out there like that - it just takes a while to find them.

So, I've built and tested this module along with several other modules (DUSG, Active Real Ringmod, VCAX2)
The only thing is while calibrating the VCO, i moved the fine and course knobs around a bunch to get in tune- my question is, can i move the knobs back to center position and simply turn the zero *trim to the right spot without losing my span? i would hate to tune this thing again.. it was a nightmare so im hesitant to just go for it.

edited in case others get confused by the questionLast edited by jbaken on Tue Apr 10, 2012 11:20 am; edited 1 time in total

- Pretty terrible packaging. All the pins are quite bent and one of the units had two pins broken on arrival. Fixable with some ugly soldering job but annoying.

- I tested a couple with my DMM - number one Hfe of the pair tested around 540 for each side ( not sure how accurate the measurement is ), number two tested around 495 for each side which is just a touch below the spec ( does it matter ? ) if I'm reading the sheet correctly - but again it's probably within the error tolerance of my DMM.

So as far as I can tell from my noob's point of view they seem genuine and it's a pretty good deal. Maybe I should have kept it to myself

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